Abstract

If you live in a place that gets cold in the winter, you have probably seen trucks out spreading a mixture of sand and salt on the streets after a snowfall to help de-ice the road. Have you ever wondered how this works? This basic chemistry project can give you some clues.

Objective

To determine which added material will make ice melt fastest.

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Credits

Andrew Olson, Ph.D., and Teisha Rowland, Ph.D., Science Buddies

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Introduction

If you have ever made homemade ice cream the old-fashioned way using a hand-crank machine, you probably know that you need ice and rock salt to make the cream mixture cold enough to freeze. Similarly, if you live in a cold climate, you have seen the trucks that salt and sand the streets after a snowfall to prevent ice from building up on the roads. In both of these instances, salt is acting to lower the freezing point of water, and changing what phase of matter the water is (i.e., turning solid ice into liquid water).

For the ice cream maker, because the rock salt lowers the freezing point of the ice, the temperature of the ice/rock salt mixture can go below the normal freezing point of water. This makes it possible to freeze the ice cream mixture in the inner container of the ice cream machine. For the salt spread on streets in wintertime, the lowered freezing point means that snow and ice can melt even when the weather is below the normal freezing point of water. Both the ice cream maker and road salt are examples of freezing point depression.

Table salt (technically sodium chloride, or NaCl) when mixed with water is an example of a chemical solution. In a solution, there is a solvent (the water in this example), and a solute (the salt in this example). A molecule of the solute dissolves (goes into solution) because the force of attraction between the solute molecule and the solvent molecules is greater than the force of attraction between the molecules of the solute. Water (H2O) is a good solvent because it is partially polarized. (This polarization is caused by the distribution of electrons in the water molecule; specifically, its hydrogen ends have a partial positive charge, and the oxygen end has a partial negative charge.) Because water molecules are partially polarized, it is possible for them to arrange themselves around ions (which are molecules or atoms that have a charge), like the
sodium (Na+) and chloride (Cl-) ions that make up table salt. This is why there is a greater attraction between the water molecules and the molecules of salt than there is between the molecules of salt by themselves, and why the water can dissolve the salt to create a salty solution.

Other substances when mixed with water can also lower its freezing point. The amount by which the freezing point is lowered depends only on the number of molecules dissolved, not on their chemical nature. This is an example of a colligative property. In this science project, you will investigate different substances to see how they affect the rate at which ice cubes melt. You will test substances that dissolve in water (i.e., soluble substances), like salt and sugar, as well as a substance that does not dissolve in water (i.e., an insoluble substance), specifically sand. Which substances will speed up the melting of the ice?

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Materials and Equipment

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Identical bowls or saucers (4)

Ice cubes (12). They should all be the same size and shape.

Salt (¾ tsp.)

Sugar (¾ tsp.)

Sand (¾ tsp.)

¼ teaspoon measuring spoon

Timer or clock

Refrigerator. You will want an empty shelf that can hold all four bowls, unstacked, at the same time.

50 mL graduated cylinder, or smaller size.

Large cup with a spout, such as some measuring cups. Alternatively you could use a funnel that fits in the graduated cylinder.

Optional: Masking tape and a permanent marker for labeling the bowls

Lab notebook

Downloadable display board template - only $1.99

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Figure 1. You will need these household materials, and access to a refrigerator, to do this science project. If you want to label the bowls, you will also need masking tape and a permanent marker.

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Experimental Procedure

Tip: As you do your experiment, take a few pictures of yourself in action and of your experimental setup. Use the pictures to help make your science fair display board more interesting and informative.

Get the salt, sugar, sand, and measuring teaspoon ready to use nearby.

Once you have set up the ice cubes in their bowls, you will want to quickly add the substances to the ice cubes so that they do not melt before adding the substances.

Into each of the four bowls, quickly place three ice cubes. Arrange the ice cubes so that only the corners are touching, forming a triangular shape, as shown in Figure 2, below.

Tip: If you are using ice cubes from a tray, it helps to let the tray sit at room temperature a little (for about five minutes) so that the ice cubes more easily come out of the tray and do not break into pieces.

Figure 2. Arrange three ice cubes in each bowl so that just the corners of the ice cubes touch each other.

Carefully sprinkle ½ teaspoon (tsp.) of salt over the ice cubes in one bowl, as shown in Figure 3, below. Then sprinkle ½ tsp. of sugar over the ice cubes in another bowl, and ½ tsp. of sand over the ice cubes in the third bowl. Do not sprinkle anything over the ice cubes in the fourth bowl — it will be your control.

Figure 3. Sprinkle salt, sugar, sand, or nothing over the ice cubes in each bowl.

Move each bowl to an empty shelf in the refrigerator. If any of the ice cubes no longer form a triangular shape in their bowl, gently nudge the ice cubes to make a triangle again.

You are doing this experiment in the refrigerator because it is easier to see the effects of colligative properties at colder temperatures. To think about why this is, imagine melting an ice cube on a hot, paved road compared to melting it in the refrigerator. The hot temperature of the road will make all of the ice cubes melt very quickly, which makes it harder to see the relatively minor effects of colligative properties on how fast the ice cubes melt.

Note the starting time in your lab notebook. Tell other people who may use the refrigerator that you are doing a science project and to not leave the refrigerator door open long as this could change the temperature of the refrigerator.

Check on the ice cubes every hour. When the ice cubes in one of the bowls have become at least half melted, take out all four bowls from the refrigerator and move on to step 7. (Be sure to take the bowls out before the ice cubes in two or more bowls have completely melted.)

Depending on how cold your refrigerator is, it may take about four hours for the ice cubes to become at least half melted.

While you are waiting, make a data table like Table 1 in your lab notebook.

Substance

Amount Melted (mL)

Amount Remaining (mL)

Total Amount (mL)

Percentage Melted

Salt

Sugar

Sand

Nothing

Table 1. Make a data table like this one in your lab notebook to record your results in. Note that the liquid measurements should be recorded in milliliters (mL).

Carefully pour the liquid water from one of the bowls into a cup with a spout, such as a large measuring cup. Make sure the ice cubes stay in the bowl, but get as much liquid into the cup as possible. Then carefully pour the liquid from the cup into the graduated cylinder. Record how much liquid was in the bowl (the amount of ice melted) in the data table in your lab notebook. After recording your results, clean out and dry the cup and graduated cylinder.

Alternatively, you could use a funnel instead of a cup with a spout and funnel the liquid directly into the graduated cylinder from the bowl.

Repeat step 7 with the three other bowls.

When pouring the liquid from the bowl with the sand, try to leave as much sand in the bowl as possible.

Now let the ice cubes completely melt in their bowls (you can leave them at room temperature). Once all of the ice cubes are melted, repeat steps 7–8 (but this time you will not need to worry about keeping the ice cubes in the bowls). Record the amount of liquid remaining in each bowl in your data table.

Calculate the total amount of water (originally in ice cube form) that was in each bowl. To do this, add the "amount melted" to the "amount remaining" for each bowl. Record the total amount for each bowl in your data table.

For example, if the amount melted was 65 mL and the amount remaining was 25 mL, the total amount would be 90 mL.

Calculate the percentage of ice that was melted (when you first took the bowls out of the refrigerator) for each bowl. Do this by dividing the amount melted by the total amount.

For example, if 65 mL was melted, and the total amount was 90 mL, dividing 65 mL by 90 mL would give you 0.72, which is the same as 72%. This means that 72% of the ice melted.

Clean out and dry the bowls. Then repeat steps 1–11 at least two more times so that you have done at least three trials total.

Did any of the substances you tested consistently speed up the melting of the ice (compared to the melting rate of plain ice cubes with nothing added)? If so, can you explain your results?

Now you are ready to create your science fair display board! If you need help making your display board, a downloadable display board template for this project is available for purchase below. The template provides step-by-step guidance for creating all the usual sections of a display board: title, abstract, background information, question, hypothesis, variables, results, conclusions, and acknowledgements.

Downloadable display board template - only $1.99

Make a great display board with the downloadable template that is customized for this project.

Get printable templates for each section of your display board.

Save time with preformatted data tables and pre-set font sizes that look good on a display board.

Just enter your project information and data, print, and attach to the display board!

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Variations

Does the melting rate depend on the amount of solute added? Design an experiment to find out.

Investigate the effect of temperature on how colligative properties melt the ice cubes. To do this, try your experiment at different temperatures, such as room temperature or outside on a hot day. Be sure to monitor the temperature regularly throughout your experiment.

Do other substances help melt the ice cubes more quickly or slowly? Identify some substances to try and then repeat this experiment.

Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

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